In order to get the details of flow in the cooling fan of a turbo generator and propose a reasonable scheme to optimize the fan,numerical simulation was carried out on an original model of the fan under the condition of 25 m 3 /s.The relationship between the efficiency and the setting angle or the twist angle of the vane was detected by changing the setting angle and the twist angle of the vane.The result indicates that there exists a parabolic relationship between efficiency of the fan and the setting angle or the twist angle of the vane in a certain range.The fan has the highest efficiency at a certain setting angle and a twist angle of the vane. The efficiency of the fan is improved by 15.8%after optimization.